Grammar check pls?

Hi There,

Can you check for me if I am grammatical in these sentences, pls?

Thanks for your email regarding...

Thanks for your email about....

Thanks for your email which or with regarding.... (Preposition)

We are using more water doing this way.

We are using more water by doing this way. (Preposition)

We are using more water if we do this way.

There is a budge limit or limitation. (Both words are noun here)

Cheers